Looking for logging into the Root Ubuntu 15.04 site and are not getting the correct working link for it? In such a case, you can use the links given here by searching your desired login page in the search box. If the page is present on our website then you will get all the links related to the Root Ubuntu 15.04 site. After that you can login as usual with your login credentials.
https://www.tecmint.com/enable-and-disable-root-login-in-ubuntu/
https://www.server-world.info/en/note?os=Ubuntu_15.04&p=initial_conf&f=2
https://askubuntu.com/questions/616045/whats-the-current-su-password-on-version-15-04
https://ubuntuforums.org/showthread.php?t=2306967
http://znil.net/index.php/Root_wieder_aktivieren_/_Anmelden_als_Root_per_SSH_Ubuntu_14.04?TheOrder=0
https://www.liquidweb.com/kb/how-to-add-a-user-and-grant-root-privileges-on-ubuntu-15-04/
http://amirazamrumee.blogspot.com/2015/06/how-to-enable-root-login-ubuntu-1504.html
https://www.liquidweb.com/kb/how-to-add-a-user-and-grant-root-privileges-on-ubuntu-16-04/
https://www.linuxquestions.org/questions/linux-software-2/resetting-admin-password-ubuntu-15-10-a-4175599345/
https://itsfoss.com/how-to-hack-ubuntu-password/
https://lists.ubuntu.com/archives/ubuntu-users/2015-November/283175.html
http://www.linuxandubuntu.com/home/how-to-reset-root-password-in-ubuntu
https://unix.stackexchange.com/questions/202698/how-can-i-run-a-program-as-a-root-user-when-my-ubuntu-15-04-machine-starts-up